This library lets you concatenate files (with or without their own pre-generated sourcemaps), and get a single output file along with a sourcemap.
It was written for use in ember-cli via broccoli-sourcemap-concat.
We depend on mozilla's source-map library, but only to use their base64-vlq implementation, which is in turn based on the version in the Closure Compiler.
We can concatenate much faster than source-map because we are specifically optimized for line-by-line concatenation.